Exhaust gas discharged from an internal combustion engine (for example, a diesel engine) may contain particulates such as soot. Exhaust gas containing such particulates is purified by means of collecting the particulates through use of a filter. Also, if necessary, the filter is heated to high temperature so as to burn and remove particulates having accumulated in the filter. Therefore, if the filter suffers breakage or a like failure, unpurified exhaust gas is discharged directly to the downstream side of the filter. Therefore, there has been demanded a particulate detection sensor that can detect the quantity of particulates contained in exhaust gas in order to directly measure the quantity of particulates contained in exhaust gas or to detect a failure of the filter.
For example, Japanese Patent Application Laid-Open (kokai) No. 2015-129712 discloses such a particulate sensor. The particulate sensor includes a tubular gas introduction pipe extending from the rear end side toward the forward end side in the axial direction of the particulate sensor, and a discharge electrode member which produces ions by means of gaseous discharge. The gas introduction pipe has a gas introduction opening which is located on the rear end side of the gas introduction pipe and through which a gas under measurement (target gas) containing particulates is introduced into the gas introduction pipe, and a gas discharge opening which is located on the forward end side of the gas introduction pipe and through which the gas under measurement is discharged to the outside of the gas introduction pipe. The discharge electrode member is located rearward of the gas discharge opening. This particulate sensor causes the ions produced as a result of gaseous discharge to adhere to the particulates contained in the gas under measurement within the gas introduction pipe, to thereby produce electrified particulates; and detects the particulates contained in the gas under measurement through use of a signal current which flows in accordance with the amount of ions contained in the electrified particulates discharged to the outside of the gas introduction pipe through the gas discharge opening.